For myself, living here in an extreme climate, invasiveness is a positive feature! Plants have a hard time of it, and the vigor of so-called invasive plants gives them a fighting chance. Of course, I watch where and how such plants are sited, but quite frankly the native species like salmonberry, fern, moss, and Sitka spruce are similarly invasive and have to have vigorous opposition if we want anything to eat!

I don't have a definitive opinion or answer. Also, I suspect that this area of biology, rather than being forever a pseudoscience, is just at an early stage where a lot of things are not sorted out, the basic concepts and terminology haven't yet been worked out, and prejudices abound.

Practically speaking: the mountain-valley I live in has very many acreages that were cleared from low-elevation forests in the last 70 years. Obviously, the species to be found in the fields and other clearings is different from the native forest types -- not just that the trees are mostly gone, but the ground species (due to changes in light intensity, photoperiod, ground-moisture patterns, ground temperature, etc) are very different.

In untended areas, you see a lot of bracken fern, bunch grasses, and wire grasses as ground cover.

Some of these invasives *are* a problem for the gardener in that they can out-compete food crops the gardener plants. Here I'm thinking mostly of quack grass (couch grass) and buttercup.

Other invasives don't threaten the gardener's crops too much, but are only esthetically questionable to *some* people: bindweed, Russian thistle, chickweed, and purslane, for instance.

Sorrel comes in, and some people do like to eat it in salads -- at least a little bit, or occasionally.

I'm with the school of thought that it's not a black & white subject, but very much a matter of specific situations, and shades of grey.

Dear Joel,
Yes, I agree, it is a matter of specific situations and shades of grey.

Permaculture is, in one definition, the design of high food and useful product-producing ecosystems, ones that hopefully continue to grow without much human interference. (Permanent + culture)

There is a strong modern trend of thought that anything "natural" ie not planted by humans in a given system is "better" than ecosystems in which humans have worked. Planting "native" plants is "better" than plants from other places, in this view. I would certainly agree that native plants belong in places they grow, but also want to feed people. Lettuce, carrots, squash, corn, wheat, peanuts, etc. etc. are probably not native in a given ecosystem, so provision has to be made to grow them in order to feed people.

Modern agribusiness has gone to the opposite extreme- monoculture- one plant for hundreds of miles. Most farmers no longer even grow a kitchen garden- too time consuming, cheaper to buy it at the grocery store, trucked 2000 miles from the West Coast, or South America. That is certainly unsustainable too!

I'm always looking to build plant guilds and small systems that are self-perpetuating with low input, low maintenance, and which offer beauty, food, and some medicinal qualities.

In extreme climates like mine, or for specific applications in more temperate areas, some of the "invasive" plants offer great vigor, ease of growing, and food abundance. Think blackberry jam from hedgerows, or orange daylilies growing along roadsides, or running bamboo confined in a highway median.

I guess I try to be careful not to let my own "invasives" (most of which I have deliberately planted as food-producing plants) get loose into the general environment. I think that's just a good practice.

But, also, most of what I've cultivated would not really spread much beyond my garden area. I have not seen much evidence in this region of veggies really getting loose and cropping up at any real distance from the gardens in which they were planted. Yes, it is true that bramble-fruits like blackberries would compete well and possibly spread. So might plum trees and some apples. But most of the ground-hugging veggies and fruits are actually stopped in their tracks, in my area, by the invasive quack grass -- which might even out-compete and stop blackberries! Not sure...

Flowering ornamentals can sometimes be another matter. Some of them do seem to compete reasonably well, and some do show up in odd places.

Carrots, radishes, and large-fruited strawberries are exotics in my region, but I do not find them becoming invasives -- even after a 70-95-year presence of European-type folks in this region who planted farms and gardens. In some places around here, plum trees, for instance, do become somewhat invasive. They perpetuate themselves as a species and spread somewhat.

I have a friend who is experimenting with many permanent plantings and plant guilds, and he has planted both "clumping" and "rampant" bamboo varieties -- mainly for use as materials (as is done in Asia) but also, potentially, for food (the edible shoot).

there is a huge nomenclature problem when discussing invasive species - native species can be become invasive also - so its not really exotic versus native debate - but rather human disturbance or the change of natural disturbance that can causes both exotic and native plants to become invasive -
i think the problem is not necessarily exotic vs. native but the creation of monocultural stands of species rather than the diverse stands of species that would exist in a naturally disturbed environment. an exotic species that can coexist in a diverse stand of natives is not a problem. an exotic species that takes over - out competes other vegetation and creates a monoculture is a problem - a native species that takes over and out competes other vegetation and creates a monoculture is the same problem.
these monocultures are ususally related to human activity...

Agreed, joepyeweed. As I mentioned, in my area when the hemlock-cedar-Douglas-fir-birch forest cover is removed, after a few years we have a lot of bracken fern and Oregon grape.

In field-cultivated but-later-unirrigated areas, we get bunch grasses and wire grasses. In areas we've cultivated as garden we get quack grass (couch grass) and buttercup, not to mention bindweed, Russian thistle, chickweed, sorrel, and purslane. I believe that both quack grass and Russian thistle are exotics, but a number of the others are not.

The main disturbance is the removal of the trees and their roots and natural debris, in a way that even wildfire does not do it. Then the plowing or tilling of the ground is another level of disturbance, even though a "rich healthy organic soil" can indeed be achieved.

The terminology is indeed hard to settle. But the "invasives" thing is an interesting phenomenon.

another thing to point out when talking about invasives - is the lack of natural disturbance for ecosystems such as wetlands and forests... wetlands evolved with fluctuating water levels and forests evolved with fire - mans impact on water levels and fire prevention has also caused a lack of disturbance that can lead to species creating monocultures.

maples trees are creating densly shaded forests in our area that naturally would have been kept in check by fire... the maples are shading out the understory prohibiting woodland plants and oaks and hickorys from creating new growth. the lack of understory vegetation is becoming a significant erosion problem. try to explain to people that we need to cut trees down and burn the forest to save it - sometimes its a hard sell...

It seems to me that invasives take over because Nature abhors a vacuum. If you weed out a 10x50' section, then don't plant it immediately to something you want, something you don't want is going to move in.

If you log off a section of land, the same thing will happen.

Invasives are plants that fill in gaps well. Too well if it finds a relatively bare spot. But if you keep your land covered with plants (even if it's only clover), the invasives find it harder to get a toehold, & what does tend to find a spot can be more easily removed (to put something better in that spot), than dealing with a whole acre or section of it.

Mother Nature knows what she's doing: trying to make up for the Human Beans mistakes.

your point is correct about mother nature filling in the vaccums - but the vaccuums themselves are being created by one exotic species and then being filled in by another.

in natural areas (not a lawn or garden) many "voids" are being created in the habitat by an exotic species. for example a silver maple sprouts in a hardwood savannah. the native understory cannot grow under it - so that void is then filled in by an exotic like garlic mustard. the garlic mustard then takes that opportunity to spread past beyond the void it was orginally filling and then outgrows all of the springs ephemerals in the woodland - thus creating a monoculture of garlic mustard in the spring - which then creates an even bigger void in the fall that gets filled in by something else like buckthorn or more maples and the cycle continues. some people do consider this natural selection... however a monoculture is not a natural condition and the the exotic species are not naturally occuring so its hard to let that natural selection of exotics continue knowing that the biodiversity of the natural area is degrading.

That's true, but you really can't change back to all natives & completely oust the exotics. They are here to stay (sometimes, very unfortunately).

And most people don't do any research to find out exactly which plants are native & which are exotic. For instance, lots of people here in the PNW think the foxgloves are native. Naturalized, yes, but they are from England. And that bane of the desert & plains, the tumbleweed, is from Russia.

Also, we are going by what is DESIRABLE for US. Mother Nature doesn't have such a high criteria as we do. We want stuff that is native/productive/pretty. Ma Nature isn't so picky. She wants fast growers that prevent erosion and protects the soil. She doesn't care if they are natives, exotics or from outer space.

Natives are nice, but they are hardly the be-all and end-all of anything, esp Permaculture. Try eating just true natives.

there is often a nomenclature misunderstanding when discussing invasives. not all exotic plants are invasive/aggressive and some native plants are aggressive/invasive in the altered/unaltered environment. no one ever expects to eliminate all exotic species and nor would we want to... when it comes to invasives, exotic or native... the point is trying to prevent monocultures and promote biodiversity. left unchecked many invasives, some exotic some native, will leave a monoculture of plants that cannot support a diverse community of birds, insects, mammals. monocultures are prone to disease. and in an exotic monoculture no natural creature will use it for food or cover thus leaving a void in the circle of life.

I mostly get annoyed with invasives when they're causing a problem...especially Canada Thistle and Multiflora Rose, but others are nasty too.

Sometimes an invasive is just the thing. We're planting about 1/2 mile of hardy bamboo along our roadsides (we're on a busy highway), and a few people have asked "but isn't that invasive?" I say "you bet!"

Until I got goats, I was really hating the honeysuckle vine all over the farm, but now it's perfect winter fodder (actually, they're quite fond of the thistle and rose as well). I suppose nuisance is in the eye of the beholder.

"Changes in the Land" by William Cronon is an excellent and fascinating book. He debunks the myth of pre-columbian "virgin" ecosystems. Indians essentially guided the makeup of eastern forests through passive control methods, the most significant and effective of which was intentional yearly burning. It is likely that they were partially responsible for the former dominance of American chestnut. All you have to do to spread chestnut trees is bury chestnuts all over the place. By so passively encouraging chestnut dominance you create an efficient food source for people directly through the nuts and indirectly through the feeding of game animals. That is fundamentally permaculture! GENIUS!
With regard to invasive species, it is helpful to remember that the northern half of North America was "invaded" by the current "native" species only a few thousand years after the last ice age. Certainly there was a period of ecological unrest and extremity, but it balanced itself out. The ecological history of earth is a long story of constant change and intermingling of different ecosystems. Continents come together, seas recede, land bridges form, birds bring seeds and small eggs across vast swaths of water. These species establish themselves. Many modern ecologists see this intermingling as dangerous pollution of the latest status quo, which amounts to ecological xenophobia. In the big picture, human relocation of species is no different than that which occurs naturally (indeed, how did homo sapiens manage to invade the Americas?). This disruption will happen whether we do it or natural processes do it. WE OURSELVES ARE A NATURAL PROCESS. We must simply think of ways to adapt to the the new arrangements in our ecosystems and seek to encourage the formation of a passively functioning balance that is beneficial to us, connects us to the life around us, and gives true freedom to individuals.

The thing about an invasive plant versus an aggressive plant is that the invasive plant moves to someone else's land. Dandelions are all well and good if you are homesteading in Keni but if you make your money off of Denali park then Dandelions are a real threat to your lively hood. In nearly all cases when you plant an invasive plant for function there is an agressive plant that could do the same job with at least 95% of the effectiveness without being a permanent problem for someone else that they cannot possibly stop.

I think the issue is how much damage is done to native plant species that are having a hard time hanging on in the face of human-based disturbance. Disturbance from natural sources is one thing, but when humans bring new species in, we often bring those which might not ever make it without our help. Then what happens to the natives?

Leucaena is a highly invasive exotic which invades and takes over stream lines and outcompetes every other shrub. It doesn't just occur as isolated individuals. It becomes a monoculture.

Cat's claw creeper is another. It is rampant, climbs high into the canopy, smothers everything under it and the weight brings down the tallest of trees. When there are no trees left, it simply carpets the ground with a dense vine nothing can grow through.

These are the sorts of invasive weed issues that really matter - swamping and smothering, not just infiltrating.

I recommend reading "Bringing Nature Home: How Native Plants Sustain Wildlife in Our Gardens" by Douglas Tallamy. Dr. Tallamy is an entomologist and professor at the University of Delaware so his focus is on insects. His thesis is that native bugs have evolved to eat native plants and a majority of insect species cannot subsist on exotic plants. The wildlife food chain depends on insects and bugs which eat plants and are then eaten by birds, lizards and snakes, etc. Unfortunately, human development has displaced or disturbed ~95% of native habitat which has correspondingly displaced a lot of wildlife.

Dr. Tallamy does differentiate between edible landscaping / food gardening and decorative landscaping. He suggests that for the decorative landscape around our homes we plant native flora that can support native insects.

It's an interesting and relatively quick read with quite a lot of supporting data.

I find the term "invasive" is used to mean different things. The narrowest meaning of "invasive" is non-native lifeforms that spread aggressively when imported to regions out of their natural habitat and do some kind of environmental harm.

Some refer to *ANY* non-native as invasive. That holds people up to too high a standard to be practical. (We aren't going to stop growing wheat).

Others refer to any "aggressive" plant that grows where you don't want it as "invasive. I *HATE* that misuse of the word. For one thing, we have a perfectly good word to describe those plants...weeds. It's a nice one syllable word that doesn't imply things that may not be the case. Also. in a healthy ecosystem there will be lots of aggressive natives that will fill in any land we abandon...that's a *good* thing in the long run. Often an aggressive invasive is better for wildlife, erosion etc. then our lawn. Personal convenience in terms of plants staying where you put them are real issues in gardening that are worth discussing, but let's not confuse them with environmental issues.

Organic Johnny, planting bamboo next to a highway is pure folly.
The canes will flop over when it rains or snows. I planted some next to my driveway and have regretted ever since. Many times I would have to cut it down to clear the driveway so my wife and I could go to work. Also, bamboo is very hard on a saw.
Mike

I try to stay off most of the controversial topics but appreciate this reference and Hemenway's review.

edlincoln's point about misuse of the term is thought provoking. If we use the word "invasive" for every weed, or every exotic plant, we dilute the meaning. For example, dandelions might be annoying, but they also provide pollen and nectar for beneficial insects. I don't know if they force out native plants. Dandelions' deep roots are thought to return nutrients to the soil surface. We don't use them for a food crop, but we could. I do pull them and feed them to the chickens, which eat them completely.

That is not the same as Himalayan blackberry, which does seem to invade and disrupt the Pacific NW ecosystem. That is even though the blackberries provide food for birds and bees like the flowers of those too. That includes native bees. I've been trying to remove them from my property, but I'm not in a big hurry and it's a lot of work.

I have also seen sterile buddleia disparaged, because the species Buddleia davidii is invasive and writers have speculated that sterile varieties could adapt and become invasive at some future time. But as it is, the sterile ones do not seed, they don't spread, and they are one of the few plants in my yard that bloom when they bloom. Many pollinating insects love them. Especially bumblebees. They are one of the seemingly few plants that deer and rabbits don't decimate. I consider deer invasive, even if they are native, because they can't be kept out, are highly destructive, and their numbers proliferate wildly in the absence of native predators.

I added non-native plants to my yard because they fill a niche that can be difficult to find for natives. That includes plants that produce pollen and nectar at times that natives don't, or that survive local conditions, or provide wanted food. I have Hyancinthoides, which are considered invasive, but are one of the few bulbs that rabbits and deer don't destroy. When the leaves die down in summer, they are not competing with other plants. I don't see them growing outside disturbed ecosystems.

If my area was restricted to all local natives, then it would be a fir and spruce forest. Which isn't a bad thing, but our society has chosen otherwise. The vast majority of what we grow around here is not native to the land that was once deep forest, long since gone. With the changing of climates, conditions that supported the prior ecosystem are changed, and there is no going back. Human beings are the most invasive and ecosystem-destructive species, and we are not proposing getting rid of them. I hope.

When I can, I add native plants, but I admit most of my garden is nonnative and a few would be considered invasive. But I don't think those are harmful to the environment or to local ecosystems, and they have a role.

This discussion, while fascinating, is way beyond my ken. I have just one question. Is "quack grass" the same as Ruth Stout's "witch grass?"

My front yard became overrun by some similar grass, and i could no longer garden there, after many years of lovely flower beds. I was devastated, but fate intervened, and I've moved! I brought a beloved fern with me, and I'll be danged, there was a sprout of that damn grass! I crucified it and left it to dry in the sun on the driveway, then disposed of it.

Just wondering about the names of these horrendous, below ground, root-invading grasses. The yard looks nice with it. But it's useless for anything else.